1. Field of the Invention
The present invention relates to a metal seal ring suitably used at pipe connection portions in exhaust pipe systems of automobile internal combustion engines for example and a method of producing the same.
2. Prior Art
A metal seal ring comprising a metal ring having a pipe-shaped cross section filled with a heat-resistant composite gasket material is used to seal connection portions, such as the connection portion between the exhaust manifold and the exhaust pipe, and the pipe connection portion between the exhaust pipe and the catalytic converter or the muffler of an automobile engine.
Such a metal seal ring is produced by a method shown in FIG. 10, a view illustrating a production process. More specifically, a sheet 1 of a heat-resistant composite gasket material 3, such as graphite, having a reinforcing core material 2, such as a perforated steel plate, therein is first prepared (FIG. 10a). The sheet 1 is stamped into a ring plate 10 (FIG. 10b). A predetermined number of the ring plates 10, two ring plates for example, are overlaid with one another (FIG. 10c). A one-side opened metal ring 7 made of a metal sheet and having a J- or U-shaped cross section and two leg portions 7a and 7b opened and extended nearly in parallel (FIG. 10d) is filled with the overlaid ring plates 10. Next, the leg portions 7a and 7b of the one-side opened metal ring 7 are bent so as to close the open end of the metal ring 7, thereby forming a closed pipe ring 8 (FIG. 10e).
In the conventional metal seal ring produced by the above-mentioned production method, the composite gasket material 3 used to fill the metal ring 7 is obtained by stamping the sheet 1 into the ring plate 10. From the entire area of the sheet 1, the area to be stamped and used for the ring plate 10 is small and a large amount of stamping waste is generated. The utilization efficiency of the sheet 1 is thus low, causing the problems of a waste of material and high costs of products.